Re: RBD read performance in Giant ?

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can you try to disable rbd cache ? (which is enable by default in giant)

[client]
rbd_cache = false


----- Mail original ----- 

De: "Florent Bautista" <florent@xxxxxxxxxxx> 
À: ceph-users@xxxxxxxx 
Envoyé: Vendredi 14 Novembre 2014 11:54:19 
Objet:  RBD read performance in Giant ? 

Hi all, 

On a testing cluster, I upgraded from Firefly to Giant. 

Without changing anything, read performance on a RBD volume (in a VM) has been divided by 4 ! 

With Firefly, in the VM (/dev/vda is a Virtio RBD device) : 

hdparm -Tt /dev/vda 

/dev/vda: 
Timing cached reads: 20568 MB in 1.99 seconds = 10314.48 MB/sec 
Timing buffered disk reads: 1190 MB in 3.00 seconds = 396.49 MB/sec 


With Giant : 

hdparm -Tt /dev/vda 

/dev/vda: 
Timing cached reads: 20340 MB in 1.99 seconds = 10199.48 MB/sec 
Timing buffered disk reads: 318 MB in 3.00 seconds = 105.85 MB/sec 


Write performance is the same than before, no change. 

How can we explain this ? 

Every system is running Debian Wheezy. 

Thank you a lot. 

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